• World Wide Web (WWW)

• Hypertext Transfer Protocol (HTTP)

• E-Mail and E-Mail discussion groups

• Usenet News

• Chat and instant messaging

• FTP

• Telnet

• E-Commerce

The World Wide Web

• Like an Internet library with millions of

books and documents

• Non-Linear structure (documents read in

any order)

• Navigate by clicking on Hypertext links

Features of the WWW

• Graphical

• Easy to use

• Cross platform

• Distributed

• Dynamic

• Interactive

Hypertext and HTML

• Hypertext – method of presenting

information. Selected words can be

expanded using links to other documents

• HTML (Hypertext Markup Language) –

used to create WWW pages and links

Hypertext Transfer Protocol (HTTP)

• Set of rules governing transfer of hypertext between computers

– Based on client/server principle

– Allows “computer A” (client) to establish connection to “computer B” (server). Server accepts connection and returns a response

– HTTP request identifies what client wants and instructs server on “action”

• WWW encompasses all information available via HTTP

URL (Uniform Resource

Locator)

• URL – address of www pages

For example: http://www.computing.dcu.ie

Web Browser

• Needed to view WWW pages

• Application program enabling user to view

and interact with information on WWW

• Client program using HTTP to make

requests to Web servers and display pages

by interpreting the HTML

Web Server

• Program that runs on web sites, responsible

for replying to requests from web browsers

• Required to publish and deliver information

on the WWW

Client/Server model

• Client software (Browser) runs on local computer

• Server software runs on web host

• Launch browser

– Type in URL

– Browser makes connection using HTTP

• Server then

– Accepts connection

– Sends file contents to browser

– Closes connection

Web Browser

• Interpret HTML pages, display them,

display programs, animation, graphics,

video-conferencing, download files etc.

• Create and publish web pages

• Entire suites built around browsers

• Multimedia files – helper applications

Client/Server model

• All machines on the internet are either

servers or clients

• Servers – provide services to clients

• Web servers, E-mail servers, FTP servers

etc. serve needs of Internet users

Ports

• Servers make services available using

numbered ports – one for each service

– E.g. server running Web server and FTP server,

web server typically available on port 80, FTP

on port 21

• Clients connect to service at specific IP

address on specific port number

Web Browsers

• Mosaic – first graphical browser

• Mosaic Navigator – first commercial

browser, became Netscape Navigator

• Internet Explorer (Microsoft)

• Mozilla Firefox

• Lynx – text only

• ……and there are others

Browser Errors

• ‘Server Does Not Have A DNS Entry’

• 503 Service Unavailable

• 403.9 Access Forgidden

• Spinning hourglass

• 404 Not Found

• 401 Unauthorised and 402 Forbidden

File Transfer Protocol (FTP)

• Used to transfer files (any type) from one

computer to another

• FTP sites all use Login and Password

– Anonymous FTP sites (anonymous login and

E-mail address as password) or automatic logon

– FTP runs on Client/Server model

• Windows has a client command-line FTP program,

but there are other, easier to use programs(WinSCP)

FTP

• FTP Daemon runs on FTP server, handling all FTP transactions, asks for account name and password

• Connection command link opened

• Downloading opens second link – data connection link

– Data connection link closes automatically after data uploaded/downloaded

• File compression used for large files

• Note that there is a secure variant known as SFTP, where S stands for “Secure”.

Electronic Mail (E-mail)

• Email uses TCP/IP

• SMTP (Simple Mail Transfer Protocol)

– File attachments

• MIME (Multipurpose Internet Mail Extension)

How E-mail is delivered

– TCP/IP

– Gateways translate e-mail formats

– Routers internal/external

• E-mail software

– Mail clients –Outlook, Thunderbird, AppleMail (etc) etc.

• Create folders – search messages, address books, mailing lists

– Most e-mail software reads HTML based pages

E-Mail Servers

• Two servers run on server machine

– SMTP for outgoing mail

– POP3 (Post Office Protocol) or IMAP (Internet

Mail Access Protocol) for incoming mail

• Typical E-mail server:

E-Mail Privacy

• Encryption – public and private key most common forms

• SPAM - Unsolicited junk e-mail

• Blocking SPAM: rather hard. Software such as Spamassassin uses rules to try.

– E-mail software to filter e-mail addresses

– ISP or Email provider (GOOGLE?) blocks spammers from sending bulk mail to subscribers

E-Mail

Basic form: username@hostname.subdomain.domain

• Advantages

• Convenience

• Speed

• Inexpensive

• Printable

• Reliable

• Global

• Disadvantages

• Misdirection

• Interception

• Forgery

• Overload

• Junk

• No response

TELNET

• Provides facility for remote logins via the Internet.

• Client/Server model – client = your PC, server =

host computer. When logged in to host, client

becomes dumb terminal

• Examples – databases, library catalogues etc

• Note: telnet is old technology, text based. You

need to know how to run programs on host. Also

has secure variant: SSH

Chat and Instant Messaging

• Instant Messaging (IM) – usually just

between two people, but may be more – e.g.

Facebook Chat, Skype etc.

• Internet Relay Chat (IRC) – requires

software on client – many chat rooms

(channels)

• Though text-based, still very popular

particularly in the tech community.

Electronic Commerce (E-Commerce)

• Electronic Store – equivalent to local store

or mail-order catalogue. Lower overhead

costs (low inventory), higher distribution

costs.

• Electronic Marketing Site – provides

information about products. Inexpensive

product promotion

E-Commerce

• Information/Entertainment Provider – no

physical product – purpose to help users –

e.g. search engines – generate revenue by

selling advertising

• Customer service site – after sales service

information, FAQ’s, software updates.

Example: Federal Express or An Post for

package tracking

Other ways to communicate on

the Internet

• VOIP (Voice over internet) – phone calls

via the Internet – e.g. Skype, Google Talk

• Blogs

• Facebook

Dangers of the Internet

• Spam – unsolicited e-mail

• Malware – general term for malicious software

• Viruses – softare that can re-produce rapidly; may be designed to do damage

• Virus hoaxes – false warning of virus; may give ‘directions’ to remove files

• Worms – spread by infiltrating systems

Dangers of the Internet

• Trojans – infiltrate computer without user’s knowledge. May install ‘keystroke logger’ – capture usernames and passwords and other confidential information. Infected computer may get ‘denial of service’. Trojans do not reproduce.

• Adware - software displaying advertising on your monitor. May be included in freeware/shareware.

• Spyware – Adware which includes information tracking

• Phishing – fraudsters sending e-mails requesting personal information

Protection

• Treat unsolicited e-mails with suspision. Do not respond

• Install latest version of anti-virus software. Download patches (Windows Update)

• Install firewall

• Ingore requests for personal details

• Do not transmit personal details by e-mail

• Check your bank/credit card statements

System Protection

• Firewall - barrier, making you invisible.

Filters data in and out of network

• Proxy server – keeps requesting computer

separated from web server

To fill in the gaps

• www.howstuffworks.com

• Seach engine – such as Google

• Wikipedia – online encyclopedia